Many computer systems operate twenty-four hours per day. The system manager of such a system is frequently expected to perform management and troubleshooting tasks at any time of day or night. Because no restriction exists as to the times at which the manager's tasks may be required, the system manager often performs the tasks from remote locations, using a terminal, or computer, to communicate with the computer system.
Typically, communication between the system manager and the computer system utilizes the public-access telephone system, although dedicated, private, telephone lines are sometimes used. However, using the public telephone system requires that the system manager locate and connect with a telephone channel, which necessitates that the system manager be stationed at a fixed location during the communication.
Further, if the computer system wishes to contact the system manager through the telephone system, the manager must keep in contact with a telephone apparatus which listens for messages from the computer system.